1. Field of the Invention
The present invention generally relates to a luminescence display panel and the fabrication method thereof, and more particular, to an active matrix organic electro-luminescence display panel (active matrix OELD panel) and the fabrication method thereof.
2. Description of Related Art
The information communication industry has risen to a backbone industry in recent years, wherein various portable communication display products are counted as an development focus, in particular, the flat panel display (FPD) which functions as the important interface between man and information. Except organic electro-luminescence display (OELD), the other major kinds of FPDs are plasma display panel (PDP), liquid crystal display (LCD), electro-luminescent display, light emitting diode (LED), vacuum fluorescent display, field emission display (FED) and electro-chromic display. In comparison with the other FPD technologies, the OELD panel has the upper hand in self-emitting, no viewing angle dependency, electricity-saving, simpler process, low-cost, lower temperature operation range, fast responding and full colorization, so as to be overwhelming in application potential and expected to play a major role for the next generation FPD.
FIG. 1 is the schematic drawing of a conventional driving circuit. Referring to FIG. 1, a conventional driving circuit 100 is coupled with a higher voltage source VDD and a lower voltage source VCC to drive an organic electro-luminescence device OEL. The conventional driving circuit 100 includes a scan line 110, a data line 120 and a control unit 130, wherein the control unit 130 is electrically coupled to the scan line 110, the data line 120 and the higher voltage source VDD, while the organic electro-luminescence device OEL is electrically coupled between the control unit 130 and the lower voltage source VCC. Usually, the higher voltage source VDD is a positive voltage and the lower voltage source VCC takes normally 0V (the grounded status).
It is clear from FIG. 1, the control unit 130 in the driving circuit 100 comprises two thin film transistors (TFTs) T1 and T2 and a capacitor C. The TFT T1 has a gate G1, a source S1 and a drain D1, the gate G1 is electrically coupled to the scan line 110 and the drain D1 is electrically coupled to the data line 120. The TFT T2 has a gate G2, a source S2 and a drain D2, the gate G2 is electrically coupled to the source S1, the drain D2 is electrically coupled to the higher voltage source VDD and the source S2 is electrically coupled to the organic electro-luminescence device OEL. Noticeably, in the conventional driving circuit 100, the capacitor C is electrically coupled between the gate G2 and the drain D2.
When a scan signal Vs CAN arrives at the scan line 110, the TFT T1 would be on and the data signal VDATA delivered by the data line 120 would be applied to the gate G2 of the TFT T2 via the TFT T1. The voltage signal VDATA applied to the gate G2 can control a current I flowing through the TFT T2 and the organic electro-luminescence device OEL, so as to control the luminance thereof. While the voltage signal VDATA delivered by the data line 120 is applied to the gate G2, the voltage signal VDATA also charges the capacitor C with a reference voltage of the higher voltage source VDD. In other words, as the data signal VDATA is applied to the gate G2, the capacitor C records down the voltage between the G2 and D2 terminals of |VDATA-VDD|. Theoretically, as the TFT T1 is off, the capacitor C is able to effectively keep the voltage |VDATA-VDD| applied to the gate G2 of the TFT T2 for a predetermined time length; but after a long term operation, the voltage Vs at the source S2 of the TFT T2 would drift up, which makes the voltage difference Vgs between the gate G2 and the source S2 gradually less and causes the luminance of the organic electro-luminescence device OEL decayed.
It can be seen from the above described, the control unit 130 in the driving circuit 100 is still unable to stably control the current I flowing through the organic electro-luminescence device OEL.